Parse environment variables into $TYPO3_CONF_VARS

additional.php_or_AdditionalConfiguration.php

<?php

defined('TYPO3') || die();

/**
 * Sets environment variables from the shell environment of the user (e.g. used with docker --environment=), from
 * webserver's virtual host config, .htaccess (SetEnv), /etc/profile, .profile, .bashrc, ...
 * When a .env file and the composer package helhum/dotenv-connector is present, the values from .env are also present
 * in the environment at this stage.
 */
(static function(array $from, array $allowedVariables) {
    /**
     * Parse environment variables into PHP global variables. Any '__' in a key will be interpreted as 'next array level'.
     * An example would be: TYPO3_CONF_VARS__DB__Connections__Default__dbname=some_db
     *
     * Conversions in keys:
     *   '_bs_' -> '\'
     * Conversions in values:
     *   Numeric values -> integer
     *   'bool(false)' => false
     *   'bool(true)' => true
     *   'array()' => []
     * @param array<string,string> $from the array which shall be watched for keys that are matching $allowedVariables
     * @param string[] $allowedVariables the names of variables in $GLOBALS that shall be imported
     */
    foreach ($from as $k => $v) {
        $keyArr = explode('__', $k);
        if (in_array($variable = array_shift($keyArr), $allowedVariables)) {
            $finalKey = array_pop($keyArr);
            $finalKey = str_replace('_bs_', '\\', $finalKey);
            for ($level = &$GLOBALS[$variable]; $nextLevel = array_shift($keyArr);) {
                $nextLevel = str_replace('_bs_', '\\', $nextLevel);
                if (!isset($level[$nextLevel])) {
                    $level[$nextLevel] = [];
                }
                $level = &$level[$nextLevel];
            }
            if ($v === 'bool(false)') {
                $v = false;
            } elseif ($v === 'bool(true)') {
                $v = true;
            } elseif ($v === 'array()') {
                $v = [];
            } elseif (is_numeric($v)) {
                $v = (int)$v;
            }

            $level[$finalKey] = $v;
        }
    }
})(
    $_SERVER,
    ['TYPO3_CONF_VARS']
);